A transient creep investigation applied to the mesoscopic analysis of plain concrete under uniaxial compression at high temperature

Abstract

A new methodology to investigate transient creep at the material level in terms of Load Induced Thermal Strain (LITS) by means of numerical mesoscopic analysis is proposed. 2D three-phase axisymmetric analyses for plain concrete cylindrical specimens are performed. Concrete phases are represented by the ITZ, the inclusions (coarse aggregates) and the matrix (cement paste including fine aggregates). The aggregates are placed using the take and place method and normal random distribution. An appropriate finite element mesh with coupled temperature-displacement is adopted using concrete damaged plasticity model in Abaqus. The numerical values are compared with a LITS semi-empirical model and experimental results available in the literature. For the analyses, LITS is uncoupled into matrix strain (dehydration of Calcium-Silicate-Hydrates), aggregate strain (geomechanical properties degradation) and mechanical strain (thermal expansion restraint). A parametric analysis is performed to investigate the sensitivity of the model due to different aggregate distributions and mechanical properties variations. A comparison of concretes with circular and polygonal aggregate shapes is performed, highlighting the main differences between the materials behavior and some challenges imposed to the model calibration. In general, a good correlation between the numerical and the experimental results was observed. The numerical model was able to represent LITS nonlinear behavior due to variations of the applied load. In addition, the numerical results, in terms of load path analysis with preloaded and preheated specimens, are in agreement with experimental observations. LITS acceleration is clearly demonstrated and the results showed that the boundary conditions play an important role in the total deformation.